Defluorination and derivatization of fluoropolymers for determination of total organic fluorine in polyolefin resins by gas chromatography

Abstract

This study presents a practical approach for determining total organic fluorine in polyolefin resins through chemical defluorination of fluoropolymers, followed by derivatization-gas chromatography. Fluoropolymers, used as polymer processing aids, are the main sources of organic fluorine in polyolefin products. These additives can be selectively extracted using tetrahydrofuran and then chemically defluorinated to release fluorine. The formed fluoride is converted to a volatile species by derivatization and detected using gas chromatography with flame ionization detection. The workflow assessment using a commercially available fluoropolymer demonstrates that this analytical approach offers a respectable linear range from 1 to 150 ppm w/w total organic fluorine in tetrahydrofuran with an R² of 0.9996, an intra-day precision of 2.6% RSD (n = 8), and an inter-day precision of 5.2% RSD (n = 7). The detection limit is 0.48 ppm w/w fluorine in tetrahydrofuran, equivalent to 9.6 ppm w/w of fluorine in a polymer sample with a sample concentration of 5 wt% polyethylene in tetrahydrofuran. Method validation was conducted using real polyethylene resins with varying fluorine levels, and the results were compared to those from two other analytical techniques: neutron activation analysis and combustion ion chromatography. While the results are generally close, some discrepancies were observed, likely due to sample heterogeneity and sample size differences. Spike recovery studies revealed good accuracy, with recoveries ranging from 90.5 to 97.8%. Cryogenic grinding of pellets into powder helps mitigate the sample homogeneity issue, providing more reproducible results. Given the widespread availability of gas chromatographs in most analytical laboratories, this method provides a practical, efficient, and cost-effective solution for determining extractable total organic fluorine in polyethylene resins and can be used for rapid screening and sample prioritization.